Polyesters are widely used owing to their excellent moldability, mechanical properties, heat-resistance, chemical resistance, creep resistance, impact resistance, rigidity, etc. Silicon wafers composed of polytetramethylene terephthalate (which may be abbreviated hereafter as PBT) are already in use.
Polyester is easily electrified by rubbing, peeling, etc. Various troubles may take place by the static charge accumulated on a molded article by electrification. For example, accumulated static charge may cause the generation of electric shock in use and the deposition of dust on the surface of the article.
It is known that a polyester can be imparted with antistaticity by the addition of an antistatic agent.
The antistatic treatment by the addition of an antistatic agent can be carried out by coating or internal addition. The coating process necessitates an additional step and, accordingly, the internal addition is preferable from the view point of production process.
Kneading of a low-molecular ionic surfactant such as an alkylsulfonic acid salt or an alkylbenzenesulfonic acid salt into a polymer is known as an internal addition process. A process to use a phosphonium salt is disclosed in the JP-A 62-230835 (hereunder, JP-A means "Japanese Unexamined Patent Publication").
Although high initial antistatic effect can be attained by the method using a low-molecular ionic surfactant because of the bleeding of the surfactant on the surface of the molded article, the process has a problem of losing the antistatic effect by the wiping or washing of the article.
A silicon wafer carrier composed of polytetramethylene terephthalate and carbon fiber is disclosed in the JP-A 8-88266 as a silicon wafer carrier having antistaticity, describing that the silicon wafer carrier has static charge dissipating property, i.e. antistaticity and gives little generation of particulate contaminant caused by friction.
A silicon wafer carrier is used after various treating procedures comprising an annealing step to remove the strain of the silicon wafer carrier, a degassing step to remove the residual volatile components, a washing step to remove attached contaminant and a subsequent drying step.
The silicon wafer carrier is used for the transportation and storage of a silicon wafer in the heat-treating step and the washing step of the silicon wafer under various conditions.
A polyether ester amide is known to have good antistaticity, however, the use of the polymer together with other thermoplastic resin causes laminar peeling and the production of a molded article having desirable mechanical properties is difficult.
A polyester composition composed of a polyester, a polyether ester amide and a modified vinyl polymer is disclosed in the JP-A 9-12844 as a composition having excellent impact resistance.